A speed limit on tachyon fields from cosmological and fine-structure data

TL;DR

This paper constrains the rolling tachyon model using cosmological and fine-structure data, showing most evolutions are excluded and that the model behaves like a cosmological constant or test field.

Contribution

It provides the first comprehensive constraints on the tachyon model from combined cosmological and fine-structure measurements.

Findings

|1+w_0| < 10^{-3} from cosmology

|1+w_0| < 10^{-9} from fine-structure data

Most allowed evolutions are slow and resemble a cosmological constant

Abstract

The rolling tachyon is a non-canonical scalar field model well motivated in string theory which naturally predicts variations of the fine-structure constant. Such variations can in principle lead to interesting observable consequences, but they can also lead to extremely tight constraints on these kinds of models. In this work we subject the rolling tachyon model evolving in a variety of potentials to current data and show that most cosmologically interesting evolutions are already strongly excluded. We find $|1+w_0| < 10^{-3}$ from cosmological data and $|1+w_0| < 10^{-9}$ from fine-structure data, leaving the rolling tachyon to either play a role almost entirely equivalent to a cosmological constant or that of a test field. We also find that in most of the allowed parameter space the field evolves very slowly, allowing its evolution to be approximated as an equivalent canonical scalar field.